try {
      diff1.entriesInCommon().put(7, "x");
      fail();
    } catch (UnsupportedOperationException expected) {
    }
    try {
      diff1.entriesOnlyOnLeft().put(7, "x");
      fail();
    } catch (UnsupportedOperationException expected) {
    }
    try {
      diff1.entriesOnlyOnRight().put(7, "x");
      fail();
    } catch (UnsupportedOperationException expected) {
    }
  }